|Hirschi, Kendal -|
|Morris, Jay -|
|Tarpley, Lee -|
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 7, 2012
Publication Date: February 1, 2013
Citation: Hirschi, K., Morris, J., Pinson, S.R., Tarpley, L. 2013. Got Rice? Enhancing Nutritional Qualities in Rice Regimes. 35TH Rice Technical Working Group Meeting Proceedings, February 27-March 1, 2012, Hot Springs, Arkansas. CDROM Technical Abstract: Humans and animals acquire minerals exclusively through dietary intake. These bioavailable minerals affect various developmental processes including bone formation, immune function and calcification. Although mineral bioavailability from fruits, vegetables and grains has been studied for decades, we know little regarding what entities define the structural, organizational, cell biological, or molecular determinants of their bioavailability from plant matrices. Biofortified foods offer a potentially powerful intervention tool that targets the most vulnerable people (resource-poor women, infants and children). Recent reviews have highlighted the benefits of these foods and the various risk factors of such an approach. However, few studies have measured the most important parameter to determine the eventual successes of conventionally bred foods or genetically modified lines; namely, are these foods actually functional foods with the enhanced minerals being available for human or animal digestion and absorption? Seed of two pure line varieties, ‘Lemont’ and ‘TeQing’, were analyzed using ICP-MS for grain concentrations of 16 elements of nutritional or antinutritional interest including Zn, Ca, Mg, Fe, K, and As. These genotypes were selected for study because they are the parents of two important rice gene-mapping populations. Among the elements differing most significantly in grain concentration between these two parental lines was Zn, with Lemont grains having up to 55% higher concentration of Zn than TeQing. This relationship held true for both milled and unmilled grain samples. What was not yet known was whether the increased Zn found in Lemont grains was in a bioavailable or a non-digestible form. The mouse has become the pre-eminent mammalian model for mineral bioavailability studies because of the underlying biological similarity to humans, the emerging genomic sequence data and the ability to manipulate the mouse genome in a targeted or random fashion. We have modified protocols previously used in rat feeding studies for analyzing calcium bioavailability in mice using radioisotopes of calcium. However, this approach cannot be used to measure Zn bioavailability. Here we harvest tissue from mice after they have eaten various diets and measure the ionome content in the tissue. Ionomics is the quantitative and simultaneous measurement of the elemental composition of tissues, and of changes in this composition in response to physiological stimuli, developmental state and genetic modifications. Here we report the ionome as an inference of bioavailability in various mice tissues after feeding rice diets that vary in zinc content. To determine the bioavailability of minerals and nutrients from rice grain, we used a modified rodent chow and subsequent ionome analysis of liver and spleen tissues. C57/BL6 mice were stratified at 42 days of age and fed either normal chow or two different minimal rice chows. These diets used grains of either Lemont (high Zn) or TeQing (low Zn) rice harvested from 2005 research plots that were milled then ground. Sucrose, corn oil and casein were added to the ground rice powder at 10%, 7% and 15% (w/w) respectively to provide simple sugars, fat and protein to the test diets. The diets were isocaloric. Mice were weighed at the beginning of feeding and after 21 days consuming the rice diets. After 21 days the mice were euthanized and tissues removed. The liver and spleen were placed in microcentrifuge tubes and dried at 70 C for 24 hours. After drying, the samples were ashed in a muffle furnace at 500 C for 16 h. The remaining inorganic materials were dissolved in 0.1N HCl. The samples were then analyzed by ICP-MS to determine the concentrations of various minerals. The mice fed the Lemont minimal diets gained slightly less weight than control animals while the TeQing diet produced animals with similar weights as the controls. The concentrations of minerals in the mouse livers was similar between the control and TeQing diets while the Lemont diet produced higher concentrations of zinc, magnesium, calcium, potassium, phosphorus and sodium. Liver concentrations of iron from both treatment diets was lower compared to those from animals fed normal chow. Concentrations of zinc, calcium and iron in the spleens of mouse fed the two rice diets was much lower compared to normal chow diets. There was little difference in sodium or magnesium concentrations among the three diets. The present study suggests that the differences in Zn concentration between Lemont and TeQing equate to differences in bioavailability. From this observation, we posit that is a worthwhile scientific endeavor to identify QTLs associated with grain element concentrations among the Lemont x TeQing and other mapping populations because these differences appear to reflect traits important not just for nutrient composition but also for nutrient bioavailability.